The invention relates to a crusher that comprises a box-like frame with two end walls and two side walls connecting the end walls; at least one crusher rotor that is supported for a rotating movement inside the crusher frame against its end walls; the circumference of the crusher rotor having a plurality of crusher teeth, and the crusher having counter-blade structures arranged to cooperate with the crusher teeth of the crusher rotor, and the material fed into the crusher for crushing being intended to be fed essentially above the centre line of the rotor(s) and to be crushed between the crusher teeth and the counter-blade structures of the crusher rotor. Typically, the present crusher comprises two parallel crusher rotors, even though nothing prevents using a one-rotor crusher.
On the basis of their running speed, crushers may be divided into two categories: fast- and slow-running crushers. Fast-running crushers are efficient, but they require that the material being crushed be free from impurities, because, due to a high circumferential velocity of the crusher rotor, their structures cannot be protected by automatically released safety means. Additional problems include fire hazard and noise and dust problems, among others.
Slow-running crushers are considerably better suited for a wider range of material to be crushed, and they also tolerate impurities. Due to a slow circumferential velocity, their capacities remain low. An increase in the circumferential velocity implies an increased risk of crusher damage, and attempts have been made to prevent this by structures whose counter-blades give way, when foreign objects that are typically of metal are caught between the crusher teeth and the counter-blade structure.
However, the above manner of preventing damage to the crusher leads to expensive solutions and, therefore, in crushers of a lower price category the damage is avoided by limiting the kinetic energy of the crusher rotor to an as low a level as possible and by making the structures strong enough to endure a sudden stop. Generally, crushers have built-in automatics, with which the rotation direction of the crusher rotor is reversed and a new crushing attempt made. There may be several of these repetitions, but finally, when an object not suitable for crushing has ended up among the material being crushed, the crusher stops and raises an alarm. After this, the foreign object is removed manually.
Solutions are known, in which the front wall of the crusher is opened around a joint in the bottom or top part of the wall, and a foreign object can be removed through the opening. In these solutions, the view to the crusher rotors often remains so narrow that it is difficult to remove a foreign object through them and the opening also cannot be utilised during maintenance, such as during the replacement of the crusher rotor.
Structures are also known, in which the entire side wall can be slid upward by means of a chain hoist. In this solution, like in the one mentioned earlier, a big drawback is that, when stopping occurs at a time, when the crusher and the feeding funnel for material to be crushed on top of it are still full of material, the material to be crushed discharges through the opening and causes various problems to the environment.
The following publications, among others, represent the prior art: US 2010252670 A1, EP 2042238 A1, DE 102006050051 A1, US 200686850 A1, U.S. Pat. No. 7,222,805 B1, U.S. Pat. No. 5,743,472 A, GB 2278788 A, U.S. Pat. No. 5,248,100 A, EP 458059 A1, and U.S. Pat. No. 4,385,732 A.